1. Field of the Invention
The present invention relates to a power supply circuit that outputs stable voltage, an integrated circuit device, a solid-state imaging apparatus, and an electronic apparatus.
2. Description of the Related Art
In order to output a desired output voltage, a power supply circuit compares the output voltage with a reference voltage and controls the On/Off of an output switching device such as an output transistor such that the output voltage is in correspondence with the reference voltage.
In such power supply circuits, a PWM (Pulse Width Modulation) control method in which the output switching device is controlled to be On or Off in a digital manner, a comparator method in which the output switching device is controlled to be On or Off, and the like are widely known. As the power supply circuits, there are a step-up type in which a voltage higher than an input voltage is output and a step-down type in which a voltage lower than an input voltage is output.
In the PWM control method, the output switching device is controlled to be On or Off in accordance with a control signal having the pulse width so as to be in correspondence with an electric potential difference, for example, during a period in which the output voltage is lower than the reference voltage.
In the comparator method, the output switching device is controlled to be in the On state until the output voltage is above the reference voltage, for example, in a case where the output voltage is below the reference voltage.
In addition, as the comparator method, for example, there is a hysteresis control method in which the reference voltage is controlled such that the reference voltage used when the output voltage is higher than the reference voltage is higher than that used when the output voltage is lower than the reference voltage by using a hysteresis comparator (see JP-A-2006-060978).
In the power supply circuits using such methods, there are cases where a soft-start circuit that slowly raises the reference voltage to be compared with the output voltage at the time of startup is disposed.
By disposing the soft-start circuit, generation of a large electric potential difference between the reference voltage and the output voltage in the power supply circuit immediately after the startup can be prevented.
In addition, in the soft-start circuit, a time constant circuit is used, in which a capacitor or the like is used (JP-A-2006-060978).